The present invention relates to integrated circuit packages, and more particularly to an integrated circuit package having beam leads approaching a bonding pad from an outer periphery of the die area.
Semiconductor chips or wafers are used in applications including integrated circuits (ICs) or flash memory, which may be used in portable electronic devices. It is desirable that a semiconductor chip hold as many circuits or memory cells as possible per unit area to minimize the size, weight, and energy consumption of devices using the semiconductor chips. ICs, whether individual active devices, individual passive devices, multiple active devices within a single chip, or multiple active and passive devices within a single chip, require suitable input/output (I/O) connections between themselves and other circuit elements or structures. These semiconductor devices are typically small and fragile and commonly carried on substrates or carrier members for support. These devices are also frequently encapsulated to protect the device from unfavorable environments, such as dust, mechanical or electrical loads, and moisture.
As the density of semiconductor chip integrated circuits increases, the density of I/O terminals, such as contacts and leads must also increase through, for example, smaller contacts and leads and/or different I/O configurations. Chip-scale packages (CSPs) offer one advantageously compact geometry, typically providing a package having an area less than approximately 1.5 times the size of the die 10 and a perimeter size roughly between 1.0 and 1.2 times the size of the die 10. CSPs find particular applicability in portable devices such as pagers, camcorders, cell phones, cameras, personal information managers, laptop computers, and global positioning devices, where size and weight are important considerations. Of these chip-scale packages, one increasingly important high density I/O configuration is a micro-ball grid array (xcexcBGA) package. FIGS. 1 and 2 illustrate a chip-scale xcexcBGA package.
FIG. 1 shows a cross-section of the xcexcBGA package including a die 10, an elastomer or epoxy-based thermoset adhesive 20 applied to a lower surface of die 10, and a tape or sheet-like interposer 30, such as an insulating organic film of polyimide. The tape 30 has an adhesive 25 formed on one side and also has metal traces or wirings 40 formed thereon or embedded therein. The metal traces 40 may be formed, for example, by depositing a thin metallic film on the tape 30 and wet-etching the metallic film. At one end, each of the metal traces 40 is attached to a respective die bonding pad 60. The traces 40 are routed across tape 30, as shown in FIG. 2, to terminate in a conductive land 45. The lands 45 collectively form a matrix pattern and vias or holes 50 are formed in the tape 30 to overlie these lands 45. As shown in FIG. 1, conductive balls 65 such as solder balls are formed in vias 50 to contact lands 45 and permit electrical connection of the I/O terminals or bonding pads 60 of the die 10 to corresponding bonding pads disposed on the surface of a printed circuit board (PCB) or other substrate. The pitch, a distance from a center line of one ball to a center line of an adjacent ball, is designated by P. An encapsulant 80, such as an epoxy thermoset, is provided to protect the electrical connections from damage caused by unfavorable environments, such as described above.
As shown in FIG. 2, tape windows 70 are selectively formed at either end of die 10 in areas corresponding to the die I/O bonding pads 60. Subsequent to connection of tape 30 to die 10, traces 40 are connected to bonding pads 60. One approach to connecting trace 40 and bonding pad 60 is xe2x80x9cwire bondingxe2x80x9d, wherein a separate wire is used to connect a bonding pad provided at an end portion of trace 40 to bonding pad 60. The separate wire is bonded to each of the bonding pads by bonding means including ultrasonic bonding, thermal bonding, and compression bonding. Another approach to connection of traces 40 and bonding pads 60 which is better suited for the particular design constraints of xcexcBGA and limitations of conventional manufacturing equipment is a xe2x80x9cbeam leadxe2x80x9d connection illustrated by FIGS. 1 and 2. The beam lead connection is achieved by forming a portion 55 of each trace 40 to project into tape window 50 and overlie a position to be occupied by a bonding pad 60. When a die 10 is disposed in a die receiving area of tape 30, the bonding pads 60 are exposed within the tape window 50 and are displaced (e.g., vertically) from a projecting portion 55 of a corresponding trace 40. The projecting portion 55 is mechanically deformed (e.g., vertically) to contact a bonding pad 60, where it is bonded to the bonding pad 60 by conventional bonding techniques and tools, such as an ultrasonic wedge bonder or thermode, to form a beam lead connection.
However, despite its advantages, xcexcBGA packaging is not as robust as conventional packaging and die evolution to increasingly smaller die sizes, particularly to CSPs, imposes additional constraints on design, manufacture and reliability of the die packaging. One important parameter is the bending profile of the beam lead, the exposed portion of the trace 40 extending into the tape window 70 to contact the die 10 bonding pad 60. If the bending profile, such as the radius of curvature of the points of beam inflection, is too severe hairline cracks may develop and lead to device failure. Conventionally, to ensure that the beam lead bending profile is maintained, a predetermined tape window 70 size or width is kept constant. Another important parameter is the length of the trace 40 between the ball and the beam lead. If the trace length is too short, difficulties in formation of the short trace adversely affect the reliability of the trace, potentially leading to circuit failure. Another important parameter is ball matrix spacing or pitch. As dies 10 evolve and shrink, the available real estate for chip-scale placement of the ball matrix also shrinks, forcing a decrease in ball matrix pitches, a distance from a center line of one ball to a center line of an adjacent ball. Presently, ball matrix pitch is maintained between about 0.40 to 0.80 mm, although it is difficult to process a 0.40 to 0.50 mm pitch economically using conventional technology. If the ball matrix
itch is decreased, the available space between balls is diminished and adversely affects routing of traces between the balls, as can be understood from FIG. 2. However, this approach advantageously preserves a desired trace length between the balls and the beam leads. Alternatively, the pitch may be maintained and the geometry or placement of the balls may instead be redistributed to utilize the available area. Disadvantageously, this alteration in the matrix geometry adversely affects tape window size and beam profile or affects the desired trace length between the balls adjacent the window and the beam leads, each potentially affecting device reliability.
Accordingly, a need exists in the art for an improved ball grid array package that permits improved ball matrix geometry while avoiding reliability concerns inherent in solutions affecting the aforementioned desired trace length, beam lead profile and tape window size.
This and other needs are met by the invention which provides, in one aspect, a tape automated bonding (TAB) tape carrier including an insulating tape having a die receiving section and a tape window formed in a portion of the tape die receiving section corresponding to a location of a die bonding pad. The tape carrier includes a conductive wiring pattern having a plurality of traces and a matrix of conductively filled vias electrically connecting a conductor filling the vias with predetermined traces of the conductive wiring pattern. At least one trace electrically connected to a conductively filled via disposed adjacent a first side of the tape window is routed to a second side of the tape window to form a beam lead projecting into the tape window from the second side.
Another aspect of the invention is a semiconductor package including a die bearing a plurality of bonding pads and a substrate connected to the die by a connecting agent, wherein the substrate includes a plurality of conductive traces forming a wiring pattern, a plurality of vias forming a matrix, and an opening at a position corresponding to the plurality of bonding pads. A plurality of conductive elements fill the vias and at least one trace electrically connected to a conductively filled via disposed adjacent a first side of the tape window is routed to a second side of the tape window to form a beam lead projecting into the tape window from the second side. The beam lead is electrically connected to one of the bonding pads.
Still another aspect of the invention includes a method for manufacturing a semiconductor package including providing a die bearing a plurality of bonding pads and providing an insulating tape including a die receiving section, a tape window formed in a portion of the die receiving section corresponding to a location of a die bonding pad, a conductive wiring pattern including a plurality of traces disposed on a side of the tape to be disposed toward the die, and a plurality of vias formed in a matrix pattern, at least one of the traces adjacent a via disposed adjacent a first side of the tape window being routed to one of a second side of the tape window to form a beam lead projecting into the tape window from the second side. In this method, the die and the insulating tape are placed adjacent one another to juxtapose the tape widow and the bonding pads and the die and the insulating tape are connected. The beam lead projecting into the tape window from the respective second side is then electrically connected to a respective bonding pad.
Additional features and advantages of the invention will become readily apparent to those skilled in the art from the following detailed description, wherein only several embodiments or applications of the invention are shown and described, simply by way of illustration of best modes contemplated for carrying out the invention. As will be realized the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.